The present invention relates, in general, to apparatus for manufacturing stock material from which flexible wall containers are made, and more particularly, to a sealing head utilizing heated air for securing lengths of resealable plastic closure strips to plastic film to produce a stock material.
In U.S. Pat. No. 3,846,209, the applicant herein disclosed a process and apparatus for securing the two halves of a conventional resealable plastic closure strip to corresponding edges of a folded plastic sheet to form a stock material web from which bags and other openable and resealable containers were to be formed. In accordance with that patent, a folded plastic film was fed from a stock roll onto a carrier which supported the film in a horizontal position. Simultaneously, a two-piece closure strip was fed from a second stock roll through a guide block which aligned the strip with a welding station. The upper ply of the folded plastic film was fed into a heat welding apparatus at the welding station where one edge of the film was aligned with one edge of the closure strip and the two edges were then welded together. The lower ply of the film web has initially folded downwardly so that it bypassed the welding station, but after the film closure strip passed out of the welding station, the lower ply was folded upwardly to coincide with the free edge of the closure strip. The film and closure strip were then fed through guide rollers and a second guide block which aligned the free edge of the closure strip with the edge of the lower ply of the film in a second welding station, where these two edges were welded together. Thereafter, the completed stock material was fed to a take-up reel for storage, or was fed to a suitable bag forming machine. In accordance with this patent, the heat-welding apparatus was of the rotary band type, having upper and lower stainless steel bands which engaged the upper and lower surfaces of the film and carried it through the heat welding unit. The actual heat welding was accomplished by a pair of heating bars which engaged the steel bands and which were maintained at the proper temperature to soften the plastic sufficiently to effect a complete weld of the closure strip to the sheet material. The heating bars were held out of contact with the plastic material by the steel bands so that melted plastic would not stick to the bars.
Although the system as described in U.S. Pat. No. 3,846,209 worked well for many years, it has now been found desirable to provide a heating system which will effect a complete welding of the closure strip to the plastic film without physical contact between the heater and the film, for such contact tends to distort or wrinkle the film, and tends to limit the rate of speed at which the film can pass through the heating station. Although steel bands were interposed between the heating bars and the film in the aforesaid patent, nevertheless it was found difficult to obtain a uniform and continuous heating and welding without occasionally overheating and burning the film. Further, it was found that when it was necessary to stop the machine for adjustment, maintenance or repairs, a great deal of waste material resulted, for usually a run of about 50 feet was required after start-up before the machine reached its operating condition and produced satisfactory welding of the fastener strip to the film.
Accordingly, it is desirable to provide apparatus for securing closure strips to a thin, flexible plastic film on a continuous basis without contact between the heating equipment and the material being heated. Although attempts have been made in the past to provide such a system, such attempts have generally been found unsatisfactory.